Supercell Structure and Dynamics
We define a supercell as a thunderstorm with a deep rotating updraft keep some supercells from producing tornadoes, even with the presence of a. Supercell thunderstorms are perhaps the most violent of all thunderstorm types, and The interaction between updrafts and the vertically-sheared environment 2: Scatter plot of strong and violent supercell tornadoes with respect to km. Supercells are a special type of thunderstorm. Difficulty in predicting which storms may produce tornadoes has differences between tornadic and nontornadic supercells in terms of . ADD and ADHD · Addiction · Alzheimer's · Autism · Depression · Headaches · Intelligence · Psychology · Relationships.
If the conditions are right, this energy creates a huge updraft into the cloud, but where does the energy come from? Clouds are formed when water vapor condenses in the air. This change in physical state releases heat, and heat is a form of energy. A good deal of a thunderstorm's energy is a result of the condensation that forms the cloud.
Every gram of water condensed results in about calories of heat -- and another 80 calories of heat per gram of water results from freezing in the upper atmosphere.
This energy increases the updraft temperature, as well as the kinetic energy of upward and downward air movement. The average thunderstorm releases around 10, kilowatt-hours of energy -- the equivalent of a kiloton nuclear warhead [source: In supercell thunderstorms, the updrafts are particularly strong.
If they are strong enough, a vortex of air can develop just like a vortex of water forms in a sink. This precursor to the tornado is called a mesocyclone, and is typically 2 to 6 miles 3 to 10 kilometers wide.
One a mesocyclone forms, there's a roughly 50 percent chance that the storm will escalate into a tornado in around 30 minutes. Some tornadoes consist of a single vortex, but other times multiple suction vortices revolve around a tornado's center. These storms-within-a-storm may be smaller, with a diameter of around 30 feet 9 metersbut they experience extremely powerful rotation speeds. The tornado reaches down out of a thundercloud as a huge, swirling rope of air.
Wind speeds in the range of to mph to kph aren't uncommon.
How Tornadoes Work
If the vortex touches ground, the speed of the whirling wind as well as the updraft and the pressure differences can cause tremendous damage, tearing apart homes and flinging potentially lethal debris. The tornado follows a path that is controlled by the route of its parent thundercloud, and it will often appear to hop.
It is more accurately called the main updraft area. This "interface" is the area between the precipitation area and the precipitation-free base. Wall clouds form when rain-cooled air from the downdraft is pulled into the updraft. This wet, cold air quickly saturates as it is lifted by the updraft, forming a cloud that seems to "descend" from the precipitation-free base.
Wall clouds are common and are not exclusive to supercells; only a small percentage actually produce a tornado, but if a storm does produce a tornado it usually exhibits wall clouds that persist for more than ten minutes. Wall clouds that seem to move violently up or down, and violent movements of cloud fragments scud or fractus near the wall cloud are indications that a tornado could form.
Mammatus clouds[ edit ] Mammatus Mamma, Mammatocumulus are bulbous or pillow-like cloud formations extending from beneath the anvil of a thunderstorm.
Supercell Structure and Dynamics
These clouds form as cold air in the anvil region of a storm sinks into warmer air beneath it. Mammatus are most apparent when they are lit from one side or below and are therefore at their most impressive near sunset or shortly after sunrise when the sun is low in the sky. Mammatus are not exclusive to supercells and can be associated with developed thunderstorms and cumulonimbus.
For most supercells, the precipitation core is bounded on its leading edge by a shelf cloud that results from rain-cooled air within the precipitation core spreading outward and interacting with warmer, moist air from outside of the cell.
Between the precipitation-free base and the FFD, a "vaulted" or "cathedral" feature can be observed. In high precipitation supercells an area of heavy precipitation may occur beneath the main updraft area where the vault would alternately be observed with classic supercells. Rear flank downdraft The RFD of a supercell is a very complex and not yet fully understood feature. The RFD of a supercell is believed to play a large part in tornadogenesis by further tightening rotation within the surface mesocyclone.
RFDs are caused by mid level steering winds of a supercell colliding with the updraft tower and moving around it in all directions; specifically the flow that is redirected downward is referred to as the RFD. This downward surge of relatively cool mid level air, due to interactions between dew points, humidity, and condensation of the converging of air masses, can reach very high speeds and is known to cause widespread wind damage.
The radar signature of an RFD is a hook like structure where sinking air has brought with it precipitation. Vault[ edit ] A vault is not observed with all supercells.
Thunderstorms and Tornadoes
The vault can only be identified visibly due to it visibly appearing to be free of precipitation but usually containing large hail.
On Doppler radar, the region of very high precipitation echos with a very sharp gradient perpendicular to the RFD.
Flanking line[ edit ] A flanking line is a line of smaller cumulonimbi or cumulus that form in the warm rising air pulled in by the main updraft. Due to convergence and lifting along this line, landspouts sometimes occur on the outflow boundary of this region.
Radar features of a supercell[ edit ] Radar reflectivity map Hook echo or Pendant The "hook echo" is the area of confluence between the main updraft and the rear flank downdraft RFD. This indicates the position of the mesocyclone, and probably a tornado. This is a region of low radar reflectivity bounded above by an area of higher radar reflectivity with an untilted updraft.
This is evidence of a strong updraft, and oftentimes the presence of a tornado. Inflow notch A "notch" of weak reflectivity on the inflow side of the cell. This is not a V-Notch. V Notch A "V" shaped notch on the leading edge of the cell, opening away from the main downdraft. This is an indication of divergent flow around a powerful updraft. Hail spike This three body scatter spike is a region of weak echoes found radially behind the main reflectivity core at higher elevations when large hail is present.
However, not all supercells fit neatly into any one category, being hybrid storms, and many supercells may fall into different categories during different periods of their lifetimes. The standard definition given above is referred to as the Classic supercell. All types of supercells typically produce severe weather.
The updraft is intense and LPs are inflow dominant storms. The updraft tower is typically more strongly tilted and the deviant rightward motion lesser than for other supercell types. The forward flank downdraft FFD is noticeably weaker than for other supercell types and the rear-flank downdraft RFD is much weaker—even visually absent in many cases.
Like classic supercells, LP supercells tend to form within stronger mid-to-upper level storm-relative wind shear,  however, the atmospheric environment leading to their formation is not well understood. The moisture profile of the atmosphere, particularly the depth of the elevated dry layer, also appears to be important  and the low-to-mid level shear may also be important.
This is because they often form within drier moisture profiles often initiated by dry lines leaving LPs with little available moisture despite high mid-to-upper level environmental winds. They most often dissipate rather than turning into classic or HP supercells, although it is still not unusual for LPs to do the latter, especially when moving into a much moister air mass.
LPs were first formally described by Howard Bluestein in the early s  although storm chasing scientists noticed them throughout the s. These storms although generating lesser precipitation amounts and producing smaller precipitation cores can generate huge hail.
LPs may produce hail larger than baseballs in clear air where no rainfall is visible. Due to the lack of a heavy precipitation core, LP supercells often exhibit relatively weak radar reflectivity without clear evidence of a hook echowhen in fact they are producing a tornado at the time. LP supercells may not even be recognized as supercells in reflectivity data unless one is trained or experienced on their radar characteristics.
High-based shear funnel clouds sometimes form midway between the base and the top of the storm, descending from the main Cb cumulonimbus cloud.